In the USA are there federal laws concerning the return of goods to a store?

Normally not federal laws but state laws most of which follow The Uniform Commercial Code. Legally stores are not required to take back items sold unless they are defective. Many stores now have very liberal return policies but that is to encourage sales by showing good faith, not necessarily to follow the law.

NO. The closest there are war laws related to warranties by the MANUFACTURER, or laws requiring stores to comply with their own stated policies.

Nothing federal, but there are a handful of state laws that are applicable depending upon the purchase and circumstances.

No. That is decided by the store's own policy of returns, whether they take them and whether they will give a refund or store credit.

Most laws governing businesses are at the state level. Return policies are policies set by the store, if you're talking about whether a store has to accept returned items or not.